Bypass kernel lockdown/UEFI secure boot on Ubuntu 18.04 with ACPI SSDT injection

Re:Bypass kernel lockdown/UEFI secure boot on Ubuntu 18.04 w... by tsimionescu on Monday June 15, 2020 @09:51AM (#23527282)

Secure boot, when working correctly, prevents the survival of rootkits. This alone is not sufficient, but it is necessary in order to allow a user of a system where a rootkit was installed to know this. Without secure boot, it is basically impossible to detect the existence of a well written rootkit, since it can control the OS tmand hide itself from any OS API, whether internal or external.

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Re:Bypass kernel lockdown/UEFI secure boot on Ubuntu 18.04 w... by AnthonyMouse on Monday June 15, 2020 @03:39PM (#23532010)

> Without secure boot, it is basically impossible to detect the existence of a well written rootkit, since it can control the OS tmand hide itself from any OS API, whether internal or external.

You can detect the existence of a rootkit by booting from known-clean read-only media and then scanning for it. It's even possible to implement "secure boot" this way without any hardware support -- have known-clean read-only boot media that contains your signing keys and then verifies and boots the operating system of your choice.

Implementing this in rushed closed-source system firmware is then purely a misfeature, along with the legitimate concern that it could lead to systems where the device owner can't install their own signing keys. Give people a USB stick with a hardware write protect switch, not signing keys hard-coded in firmware.

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Re:Bypass kernel lockdown/UEFI secure boot on Ubuntu 18.04 w... by tsimionescu on Monday June 15, 2020 @05:06PM (#23532971)

That does not solve the issue of a corrupted BIOS/UEFI, right? I assume at least that UEFI Secure Boot also protects itself from any attempt to be replaced without proper signed keys. Without this kind of protection, you either have to have a readonly BIOS/UEFI (so no possibility to issue updates), or you have a root-writeable, and so root-kit-able BIOS/UEFI.

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Re:Bypass kernel lockdown/UEFI secure boot on Ubuntu 18.04 w... by AnthonyMouse on Tuesday June 16, 2020 @11:49AM (#23540578)

You don't need all the firmware to be read-only, only the firmware update code, which can then require a hardware jumper to be set in order to update the firmware. Then the firmware can't be corrupted without physical access to set the jumper, and even if it is, the owner can still re-flash clean firmware because the update code is strictly read-only and therefore still clean.

And you already need to be able to at least detect that someone has had physical access, otherwise you can't even be sure that the device hasn't been replaced with a compromised one that forwards your credentials to the attacker.

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